The present invention relates to an IGZO oxide sintered compact that is used as a sputtering target upon producing, via the sputtering method, a transparent semiconductor IGZO film for use as an active layer or the like of a thin film transistor in a liquid crystal display device or an organic EL display device, its production method, and oxide powder that is used as the raw material for producing such an oxide sintered compact.
A thin film transistor which uses, as its active layer, a silicon-based material for driving the respective matrixes is used in a display element of an active matrix-type liquid crystal display device and the like, but the development of a thin film transistor using a transparent oxide semiconductor is being carried out in recent years due to drawbacks such as the reduction of the aperture ratio caused by the light-shielding layer for preventing the absorption of visible light, and the necessity to perform the deposition at a high temperature.
The transparent oxide semiconductor is attracting attention from the perspective of enabling low temperature deposition, high mobility and so on. Since the mobility of an amorphous IGZO film made from an In—Ga—Zn—O-based material (hereinafter referred to as the “IGZO”) having indium, gallium, zinc, and oxygen as its constituent elements is higher than the mobility of amorphous silicon, and a field-effect transistor using such amorphous IGZO film as the active layer has high expectations since it possesses favorable characteristics such as the ON/OFF ratio being high (refer to Non-Patent Document 1 and Patent Document 1).
As the method of preparing an amorphous IGZO film, the sputtering method having superior mass productivity is most appropriate, and the IGZO target needs to have high density in order to use the sputtering method.
Nevertheless, although there were cases where a high density IGZO target could be produced, the density of the sintered compact would decrease while the production is ongoing, and, if production is further continued, it was possible to achieve a high density target again. The reason for this was considered to be inappropriate target production conditions such as the sintering conditions, but ultimately the cause remains unknown.
Meanwhile, the following examples have been previously reported as the types of impurity concentration and tolerable concentration in the oxide sintered compact target.
Patent Document 2 describes a method of producing an indium oxide-based sputtering target using indium oxide powder having a chlorine concentration of 50 wtppm or less. Nevertheless, this specification only discloses the effect of the chlorine concentration contained in the indium oxide powder.
Patent Document 3 describes indium oxide powder having low halogen content, however, in the Examples, only indium nitrate is used as the raw material.
In other words, the only report concerning the impurities in the oxide sintered compact target in the prior art documents relates to chlorine or the like contained in the indium oxide powder, and there is no report concerning the influence that the type or concentration of impurities contained in gallium oxide (Ga2O3) as the raw material of the IGZO transparent semiconductor target disclosed in the present invention has on the sintered compact density.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2006-173580    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2008-308385    [Patent Document 3] Japanese Unexamined Patent Application Publication No. H10-182150    [Non-Patent Document 1] K. Nomura et al. “Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors”, Nature, 432, p 488-492 (2004)